NASA's Stardust Findings May Alter View of Comet Formation

Samples from comet Wild 2 have surprised scientists, indicating the
formation of at least some comets may have included materials ejected by
the early sun to the far reaches of the solar system.

Scientists have found minerals formed near the sun or other stars in the
samples returned to Earth by NASA's Stardust spacecraft in January. The
findings suggest materials from the center of the solar system could
have traveled to the outer reaches where comets formed. This may alter
the way scientists view the formation and composition of comets.

"The interesting thing is we are finding these high-temperature minerals
in materials from the coldest place in the solar system," said Donald
Brownlee, Stardust principal investigator from the University of
Washington, Seattle.

Scientists have long thought of comets as cold, billowing clouds of ice,
dust and gases formed on the edges of the solar system. But comets may
not be so simple or similar. They may prove to be diverse bodies with
complex histories. Comet Wild 2 seems to have had a more complex history
than thought.

"We have found very high-temperature minerals, which supports a
particular model where strong bipolar jets coming out of the early sun
propelled material formed near to the sun outward to the outer reaches
of the solar system," said Michael Zolensky, Stardust curator and
co-investigator at NASA's Johnson Space Center, Houston. "It seems that
comets are not composed entirely of volatile rich materials but rather
are a mixture of materials formed at all temperature ranges, at places
very near the early sun and at places very remote from it."

One mineral found in the material brought back by Stardust is olivine, a
primary component of the green sand found on some Hawaiian beaches. It
is among the most common minerals in the universe, but scientists were
surprised to find it in cometary dust.

Olivine is a compound of iron, magnesium and other elements. The
Stardust sample is primarily magnesium. Along with olivine, the dust
from Wild 2 contains high-temperature minerals rich in calcium, aluminum
and titanium.

Stardust passed within 149 miles of comet Wild 2 in January 2004,
trapping particles from the comet in an exposed gel. Its return capsule
parachuted to the Utah desert on Jan. 15. The science canister with the
Wild 2 sample arrived at Johnson on Jan. 17. Samples have been
distributed to approximately 150 scientists for study.

"The collection of cometary particles is greater than we ever expected,"
said Stardust Deputy Principal Investigator Peter Tsou of NASA's Jet
Propulsion Laboratory, Pasadena, Calif. "The collection includes about
two dozen large tracks visible to the unaided eye."

The grains are tiny, most smaller than a hair's width. Thousands of them
appear to be embedded in the glass-like aerogel. A single grain of 10
microns, only one-hundredth of a millimeter (.0004 inches), can be
sliced into hundreds of samples for scientists.

In addition to cometary particles, Stardust gathered interstellar dust
samples during its seven-year journey. The team at Johnson's curatorial
facility hopes to begin detailed scanning of the interstellar tray
within a month. They will initiate the Stardust at Home project. It will
enable volunteers from the public to help scientists locate particles.

After registering, Stardust at Home participants may download a virtual
microscope. The microscope will connect to a server and download "focus
movies." The movies are images of the Stardust Interstellar Dust
Collector from an automated microscope at the Cosmic Dust Lab at
Johnson. Participants will search each field for interstellar dust impacts.